Certain methods and devices for operating a drive unit, in particular of a vehicle, are conventional. The drive unit includes a power transmission unit, for example, in the form of a clutch, which in the engaged state transmits an output power of an engine to a drive train, the state of the power transmission unit being detected.
In vehicles having automatic start or repeat start in a start-stop operation, the starter must not be actuated while the drive train is engaged, but only while the drive train is disengaged, i.e., while the power transmission unit is disengaged. A neutral signal is required to control the starter, the signal being set when the power transmission unit is disengaged and thus when the starter may be enabled. This neutral signal must be validated via diagnosis. Usually an additional switch is used for validation.